What is SCROG (Screen of Green)?

Contributed by SCW:

This article is intended to provide information for new growers using the "ScrOG" or "Screen of Green" method in mini or micro cabinets under small HPS lights, in the range of 70 to 250 watts. I won't discuss the application at 400, 600 and 1000 watts, as that's outside the scope of my experience. See the "links" post below for further materials regarding 400 watt and other scrogs.

Small HPS lights

Small HPS lights are perfect for growing cannabis in restricted space conditions, as they produce the most light from a given amount of electricity of any suitable lamp for cultivation, and produce a spectrum that is favorable for flower growth. The spectrum is not the best for vegetative growth, but that isn't really important to scrog growing, as the vegetative period is so short. Lights as small as 35 watts are available by stripping components from security lights commonly available at discount hardware stores. 250 watt lights can produce as much per foot in scrog conditions as 1000 watt lights in room growing. A single 70 watt lightcan produce enough for an average pot smoker in a space as small as 1 sq. ft. MH lights are available in small sizes, but they produce less light and more heat than their HPS counterparts, and heat is an important consideration in cabinet-style growing. Regarding fluorescents, the light to heat ratio is even worse, and I am not aware of any situation in micro and mini growing where I would favor them over small HPS lights.

Note that these lights are quite weak compared to 400, 600 or 1000 watt lights used in production growing. Intensity means that the light can be father away from the plant and still be bright enough at the bud surface to produce. Intensity is necessary for tight bud formation.

To get the most out of a small HPS light, you must keep the bud sites within the productive range of the bulb, a lopsided sphere extending out from the lamp source. For a 250 watt light, that circle of light extends out about 20" from the lamp. For a 70 watt light, the maximum distance is apparently around 8" (per chthonic, who has experience with the lights). A group of tall, skinny plants under such a light would only be properly lit at the very tops of the plants, leaving the bottom parts shaded out and in a low intensity light field, producing small, lightweight buds at best.

Ideally you would like all the buds within that magic circle of light intensity, and you would like that sphere of light completely filled with buds. How can that be accomplished?

The scrog method

The essential detail of the scrog method is a screen, usually poultry netting, typically suspended between the planting medium and the lamp. The plants grow up to the screen and then are "trained" under the screen, resulting in a flat table of plant growth, a field rather than a forest. Because all the buds are growing at the same height, it is possible to get all the growth within the effective circle of light from the lamp, maximizing production from the space. It's really that simple.

Well, nothing new under the sun, the method has been used for years. In modern terms, the method was first popularized on the internet by the work of pH on the usenet group Alt Drugs Pot Cultivation, or "ADPC" for short. You can access ADPC from several web-based sources, and pH still posts there regularly. But the method as initially used by pH was designed to tweak production from a large area under fluorescent lights, like the "multi-shelf" method explained in his article on N.P. Kaye's Lycaeum site. N.P. Kaye is in fact credited with the term "screen of green", which pH shortened to "ScrOG".

I am aware of a least one grower who used scrog and HID lights before that time, based on a mention in Robert Clarke's book "Marijuana Botany", which was also a source for pH. But most work involving scrog and HID lights is quite recent. It is noted by pH that the first "yield-o-rama" post for HID scrog was in July of 1997. I became aware of the method from a medical grower in the final days of the Hemp B.C. boards, Savapalet, a posting buddy of Aeric 77.

Before discussing the method in detail, let's explore the other alternative for small HPS lights, the plantlet sea of green method.

Sea of green

The plantlet sea of green method was developed to maximize the speed of cannabis growing in limited height situations. In a typical sea of green setup of this type, clones are planted at densities as high as 9 per sq. ft. Within a short time after being established, the lights are switched to a 12 hour dark period. What happens to the planted clone?

The clone could just sit there, stretch a bit under the light regime, and flower, producing a tiny little bud with a couple of seeds. But that rarely, if ever, happens. Instead the clone takes off in a rush of growth, forming a woody main stem and branches. If the plant is suitable for sea of green growing, it will stop short of the lights and flower. Most indica dominated plants stop short enough to be grown using this method. That process is at the heart of the sea of green method, as it results in the smallest possible plant flowering in the quickest possible time.

Why does the clone act in this manner? The actual process is subject to debate. Your author suspects that the clone reads the light switch as fall, and has a mechanism that recognizes that it's too small to produce seed. So the clone goes into a furious growth mode that stops when the plant reaches a minimum height set within its genetic software, and then flowers. Others argue that the clone's response is just a variation on the normal stretching process that happens when flowering is forced in any size plant. For purposes of the discussion here, it doesn't really matter why the response occurs, just that you can rely on it.

The problem with the sea of green method under small HPS lamps is that it produces a number of small spikes under the lamp, a forest rather than a field. The plants crowd each other out and shade the lower portions, which in any event are too far from the light source. As we discussed above, tall and skinny is not productive under a small light. I grew initially using this method, based on books and magazines that I read before designing my 250 watt system, and it worked well for many years, yielding just over 1 oz. per ft. Not bad, but it can be so much better.

Note that in the mid-90's, the term "sea of green" started being applied to much larger plants and grows, even multiple 1000 watt installations over room-sized grow tables, with 3 foot plants spaced at one per foot. It seems the original meaning of the term, the SSSC plantlet method, has been almost forgotten.

Basic flat, fast scrog

The screen method used by pH relied on a long vegetative period for the plants to cover a large area of screen held close to a series of fluorescent tubes. The method I will describe here uses the same sort of growth process that occurs in a sea of green plant, and is very fast. The screen should be set about 8-12" above the planting medium, if possible. There are two purposes for that gap. First, you have to get your hands underneath the screen in order to handle the plant shoots and to remove excess growth shaded out under the screen. Second, there needs to be sufficient space for the plant to branch. Branching is essential to scrog. I prefer a space of about 10" for a 250 watt light, but some growers prefer shorter gaps for smaller lights, as little as 4-6".

Note that the screen does not have to be absolutely flat, and there are good arguments for dishing the screen to match the curvature of the light field. I don't radically dish my screen, but I do tie down the middle of the screen to prevent the screen from being pushed up, which would be counter-productive.

The clones are set under the screen at a density of about 1 plant per sq. ft. Experience in using the method with various types of plants may result in more or fewer plants, but 1 per ft. is a good starting point. Note that plant density is much lower than for plantlet-method sea of green. That means fewer clones to manage and fewer plants to be holding in a bust, a factor in sentencing guidelines.

Why clones, by the way? By the time you find out which plants are male and female from seed, it would be impossible to extract the males from the foliage wound into the screen and fill in the gaps with female shoots, without a real mess on your hands. Seed plants also waste several inches of height before a mature stem section is reached from which branching can begin, whereas clones branch right from the medium. Height control is typically a limiting factor in cabinet growing. With female seeds it may be possible to grow a predictable scrog by raising the screen height, making up for the wasted stem length. Seed plants may react differently to forcing as well. I have no experience growing from seed.

The clones are established and kicked into vegetative growth. Assuming an 8-12" gap, just about the time where the growing tips penetrate a few inches above the screen, say at two weeks, the lights are switched to a 12 hour dark period. Ideally a response similar to the sea of green method kicks in as explained above. Instead of stopping and flowering, the plants take off, filling the screen with growth. At a density of 1 plant per ft., it usually works out that the plants stop and "crown off" just as the screen is filled. It's really magic to see it happen. Note that this timing method is not universal. Different plants may require more vegetative growth, or perhaps even less. My advice is to start by forcing early, because overgrowth creates an unproductive canopy, more salad than buds.

The timing is so critical. You must be around during this period to guide the growth under the screen, and to make sure all gaps in the screen are filled, one bud site per screen hole with standard poultry netting (2 x 3 inch holes). Excess leaf growth must be removed above the screen, which usually means all the fan leaves are removed. Never mind arguments about whether fan leaves should or should not be left on plants, this is a different animal, and the rule here is, all bud sites must see the lamp in order to develop. At least in a small scrog grow, fan leaves would overwhelm the neighboring buds. Get a good sharp, clean set of pruning scissors and just leave them with the grow. You'll need them every couple of days during this period.

Training really isn't difficult. With a limber plant I usually let the shoots grow vertically above the screen and then pull them under by the stem, re-orienting the stem horizontally under the screen to line up bud sites with screen holes. You don't have to tie anything down, as the upward pressure of the stem will nail the foliage to the screen, but some growers like to tie off stems to the screen during the early phases of screen filling. Here's what one grower, Ultimate, has to say on the subject:

"I swear by twist ties and have a huge stock. They can be found just about anywhere. Purchase ties which are most flexible (wire with the smallest diameter) and coated with plastic not paper, as the paper will eventually mold.

"So why twist tie? Two reasons when training for in any screen application.

"When initially induced to 12/12, the main tip/tips that hit the netting are immediately trained 90 degrees perpendicular to the netting. This allows for the light to concentrate the most productive part of the plant, forcing the most efficient production the plant can dish out. Branches under the netting are allowed some time to reach the light, but less than half will see light because you're concentrating on efficiency. The most efficient growth will occur where the main stem bends on a 90 degree and beyond, which receives the most light.

"I like to leave the ties long enough for the plant hold the shape desired. Main stem usually around the second week (give or take) , and branches will always vary. Branches coming off the main stem parallel to the netting are spread as far from the main stem as possible making for a even canopy, more bud sites per square, and controlling overall height.

"To a certain extent the buds freeze at a certain point and height/stem length slows. The canopy height is close to being established, but some plants are more vigorous than others and continue stretch beyond the rest of the crop. When bud training the longer colas are controlled by bending and tying down to the screen with twist ties. In extreme cases crushing/crimping is necessary. Moldy buds can be avoided by repositioning buds growing against each other. By using twist ties each bud can be positioned where air flows between each cola allowing efficient light dispersal within the canopy and better air flow.

"Without ties? Yield was lower. A few larger colas had to be tied down shielding smaller buds from direct light, not to mention forcing the light to be raised higher, lowering production (This can be resolved by switching to a more intense bulb) . Some branches grew buds with LONG stems between the screen and base of the cola to compete with the large colas. Hybrid vigor in some cases, or plants which tend to "stretch" more than others eventually straighten out the 90 degree angle exposing less area of the most efficient portion on the plant and eventually stretches to a point where more stem was exposed to direct light, above the screen than desired. A view from the bottom (planter to the screen) showed that efficiency could be improved."

Some plants have brittle stems, and are difficult to train. It is possible to bend a stem by crushing it lightly at the bend. So long as the structures in the plant that carry fluids aren't damaged too much, the shoot will heal and be just fine (thanks to Uncle Ben for that trick). It may also be possible to top brittle plants under the screen, so that the future growth will be in several, more slender shoots. I have no experience in training a scrog grow by topping.

The second pruning step occurs during and after the screen is filled. All growth under the screen must now be clipped off. Shaded growth quickly shrivels and dies, leaving ideal growth mediums for mold. Excess leaves and shoots should be clipped close to the stem, to avoid leaving stumps as mold sites. Robert Clarke recommends pruning away from the stem, but a lot of the standard advice has to be discarded when dealing with the special conditions of a scrog grow. The space under the screen is dark and humid, and you want as little plant material under there as possible. You will haul out buckets of leaves and excess shoots from a scrog grow, but the plants can take it. Clip away.

Subsequent pruning is really limited once the plant sets buds and stops growing. Some plants develop large leaves from the buds themselves, and if the leaves shade out neighboring bud sites, they must be removed. But that's about it. Most of the flowering time in a scrog grow the maintenance level is near zero.

If everything goes well, the extra time required for the plants to reach the screen before the flowering period is lengthened by only about two weeks. No additional time is required to fill the screen, because that time is the same used by the sea of green method to add height. The plants end up just as long, but the growth is directed horizontally. Typically a flat scrog grow ends up resembling a tropical forest canopy, with all the buds in a thick carpet extending 8-10" above the screen. The area underneath the screen contains the tree trunks that support the canopy, like piping connecting the root mat to the canopy.

Does it matter how the canopy is created? Not particularly, in my experience. There does not seem to be a lot of difference between buds that would come from sites lower on side branches from those at the actual tip of the plant. For the most part, a bud is a bud in this method. Note that the buds grown in a scrog field are each a piece of what would be a vertical cola. Each bud grows up vertically 90 degrees from the stem. You are familiar with how a cola is made up of individual bunches of flowers connected to the stem in an overlapping spiral, producing a structure that looks like a single unit. In scrog, each one of those florets matures into a small bud in their own right, typically 4-8" tall, about the size of a cigar. They aren't donkey dicks, and you won't impress the editors of High Times into featuring your buds in the centerfold, but weight is all we're interested in, not appearance. As I say, it all looks the same in the bong bowl.

How much weight? I have shown that it is possible to reach around 2 oz. per ft. with a suitable plant and enough light density. 400 watt growers have reported up to 2.4 ounces per foot in a flat scrog. In a compressed grow, using shielded lights in a box of screen, I did nearly 2.6 ounces per foot, measured by canopy area. I suspect that 75 watts per sq. ft. is about the minimum to reach that kind of production, but I don't know for sure. Understand, that the HID scrog method has not been around very long, and results are sketchy. Your results may vary, but certainly you will do better using scrog than small- scale sea of green at any light density. As an experienced plantlet-method sea of green grower, I feel comfortable stating that as a fact.

A side note regarding the measurement and reporting of production is appropriate here. For the most part, growers on the boards talk in terms of so many ounces per square foot of growing area, apologies to the metric system. Some growers feel it is more appropriate to measure production in terms of HPS watts, taking into account how efficiently the grower uses the lamp. In cabinet growing the area under cultivation cannot be expanded, and the lamps are typically very small, especially in comparison to any kind of production grow. I believe measuring output per watt would favor underlit grows, given an equal amount of space being used. Cabinet growers want to know how to produce the greatest weight of buds in the space they have, not how to conserve lamp power. Indeed, a cabinet grower should use the greatest amount of lamp power than can be cooled. Accordingly, I favor reporting production by area, but I encourage reporting a complete set of information about the grow so that light density can be taken into account by those so inclined. A "yield-o-rama" report or "YOR" is a good compromise. You can find information about the YOR on the usenet group ADPC.

What can go wrong with a flat scrog grow? The worst thing you can do is to allow the plants to grow too long. You would think that excess growth could be cut out or moved to vertical screens, but in practice I find it's difficult to recover from a badly overgrown screen. Plants that grow into and fill the screen seem to put on better bud weight than overgrown plants that are tied down and whacked back to fit.

Bog methods

Many people have been excited about the scrog method and have dreamt up all sorts of ways to expand production, myself included in the mad scientist crowd. The most common variation is the "bog" method.

Bog for "box of green", was first coined by Kunta and further developed by chthonic and several other growers. Added to the horizontal screen are vertical screens around the perimeter. Either additional plants are used at the edges, or the scrog field plants are grown longer, but either way, the additional foliage is allowed to grow up the outside of the vertical screen, taking advantage of wasted air space above the field. It also allows plants at the edge of the field to get into the circle of intensity from the bulb.

Imagine the light field as a circle sitting tangent to a horizontal line. Imagine your plant as a point on the line outside of the circle. How can the plant get inside the circle? By going up. You might equate this method to an "arena" grow in this regard. An extension on the bog theme is spiral bog, first coined by chthonic. In a spiral bog the plants are allowed to add considerable vegetation, which is trained around the box in a laid-down spiral, like this: //////. This method allows all the screen area to be densely filled with bud sites.

There are two ways to fill the vertical bog screens, as I mentioned. The first is to use more plants, which are added to the edges of the grow. When the horizontal scrog field plants are forced to flower, the plants on the edge are allowed to grow vertically like sea of green plants, the resulting growth being trained to the vertical screens. If the growth is too tall for the screens, it can be laid down at an angle, like a spiral bog grow. The advantage of this type of bog grow is reliability and speed, since the horizontal field is filled in exactly the same manner as in a normal scrog grow. The disadvantage is that the number of plants is increased to near plantlet-method sea of green levels.

The second method is use the same number of plants as in a standard scrog grow, or thereabouts, but to allow them to grow longer before forcing, around another two weeks of growth seems to be about right. This process is proving to be tricky for me, and I have so far failed to produce a fully successful extended bog grow. But other growers are having success, and the method is superior in theory. Here's what chthonic has to say about his experiences with 70 watt HPS lights:

"The quickest and most successful approach that I have found to train a bog grow is to lower the horizontal screen to within 6" of the soil and grow 2 plants per sq. ft. straight up to the vertical training screens. As it's a box driven by a 70-watt bulb, the height from the horizontal screen to the roof is only 12". The plants grow unhindered 18" from the soil up through a narrow band of the horizontal screen and onto the verticals until they touch the roof. Then they are laid down horizontally and trained in a spiral fashion /// around the vertical training screens. Spiral bog or s/bog. The cabinet is small; spiral training is the only way to direct the shoots so it just happens...

"The spiral training can go one of two ways. The entire plant can be bent over in one direction and trained along with the rest of the plants in a clockwise or counter-clockwise fashion around the vertical training screens. Or the plant can be trained as it naturally branched, trained in opposite directions along the vertical training screens."

Any method of growing should be analyzed not only for production over the space used, but also for production over time. Just for the sake of argument, let's suppose a plantlet-method sea of green method produces 1 ounce per ft., and the subject plant takes 60 days to complete its life cycle. That would be .017 oz. per ft./day. Let's suppose a scrog grow takes two weeks longer, 74 days, and produces 1 1/2 oz. That would be .020 oz. per ft/day, advantage scrog. Let's suppose than an extended bog grow takes two more weeks than a scrog grow, 88 days, and produces 2 oz. That would be .023 oz. per ft. day., advantage extended bog.

Note that it's possible to shorten the cycle by growing plants in a separate area for about three weeks and then adding them to the scrog setup. But most micro and mini growers don't have room for a separate growing area.

The "bog" term is subject to some debate. Chthonic believes that the term should be used for a box of foliage that surrounds a light held in a vertical position. Such a setup can be an outstanding way to get the most of out small security lights in the 70-100 range. But I think for a larger light, like a 150 or 250, it is necessary for the light to be in the normal horizontal position above the box. Personally, your author thinks that bog can be used as a general term to describe such a grow, and I don't really know what other term to use. Chthonic believes this type of grow can be referred to as an arena grow, but I've usually seen that term applied to free-standing plants rather than a box of screen. In my recent compressed grows using shielded lights, I coined the terms "h/bog" and "v/bog", stealing from chthonic's notation, but no one else has picked up on the lingo. Time will tell what terms become attached to these methods. Most people just use the generic term "scrog". Fair enough.

Finally, hollow screen forms do not have to be in the shape of square-cornered boxes. I've seen one grower using small HPS lights who shaped his screen into a deep bowl shape, with the light suspended in the middle. Recently I read posts on ADPC describing inverted V shapes. A single "correct" way to do this probably doesn't exist.

At this point, these methods are so new that every grow provides significant information. My advice to those new to the scrog method is to get a few fast, flat scrog grows under your belt first to get used to the process. But do add the vertical screens regardless, and capture whatever excess growth you can on the verticals, as there is no reason not to handle as much growth as you can.

V-scrog

The final extension of this concept was thought up by Kunta, and dispenses with the horizontal screen entirely. I coined the term for the method, "v-scrog", for vertical scrog. Vertical screens extend from the plant medium all the way up to the top of the growing space. The light is not in a reflector at the top of the space, but is suspended vertically in the middle of a tube of foliage, approaching Peg's Rama concept for zero-g cannabis growing. Note that the entire light field is used, not just from the bottom half of the lamp and what comes off the reflector. The foliage area is stunning. Imagine a 2 x 2 cabinet with a v-scrog screen held 4" from the walls, with a gap in the front screen for maintenance. Suppose the buds fill up about 3' of the vertical screen. We're talking 4 screens, each 4' in area (16" x 36"). Take off a couple of inches for corner overlap and a gap in the front for access, and that's nearly 14 sq. ft. of screen in the same space that supports 4' of flat screen. Even if the production per foot were half, and it would be less due to the loss of the 3D flat scrog field, you're still talking 3 ounces per foot!

Can that really be possible? Not so far. I have grown two v-scrog's that were mostly failures, but I have modified the growing space to correct the problems and I will continue testing in the future. The problems so far involve the time needed to fill the screen area, which could reduce the production over time substantially, and the ability to handle the moisture load produced by the massive amount of foliage. I am also not the world's most talented trainer, but chthonic and Ultimate have done very well in tiny vertical box forms with 70 watt lamps.

Even if production isn't dramatically better than horizontal methods, v-scrog is a promising solution to growing in very restricted height conditions. It might be possible to grow a productive crop in as little as 2', maybe less. Since the light-to-foliage gap is horizontal, the only absolute vertical needs are for the plant container and a gap between the end of the downward-pointing bulb and the planting medium. Plant growth could be controlled by training it across the vertical screen, which could be any reasonable height.

Soil or hydro?

I have read every scrog post on this board, and a lot of the activity on other boards and at ADPC, and it appears that a successful scrog can be done using plants in pots as well as with more exotic hydroponic systems. But there are a few elements of scrog growing that tend to favor an active hyrdroponic setup.

Once you get past a small, flat scrog grow, it becomes very difficult to train a more complex grow by reaching into the cabinet space. I would never design a scrog system without the capability of rolling or sliding out the plant container and screens as a single unit. Obviously that means that the screen should be connected to the plant container, or possibly to a common substrate, like a plywood base. The screen does not need to be sturdy, it's just a guide, so there are many ways this could be done. But obviously it is much easier to slide out an empty container than one full of water (DWC) or soil.

Although I lack experience in using soil intensively, active hydro systems allow freshly rooted clones to have direct access to very high levels of nutrients immediately. That may mean that active hydro scrogs will evolve quicker than soil or DWC grows. I don't believe there is enough experience available to express a firm opinion on this matter.

Conclusion

Hopefully this will give you an idea of where we stand on small level scrog methods and will answer some of the basic questions. In spite of the long history of the use of screens and netting in cannabis growing, accelerated scrog growing under HID lights is a wide open field, and each new grower can add experience and ideas to the mix.

Editorial assistance by newbie. Additional input by chthonic and Ultimate as noted. Thanks to pH, Uncle Ben, Ganja Baron and Teahead for assistance and suggestions on specific topics. I should also acknowledge indirect input by Bongo and Shuzzit, as well as the other growers mentioned in the article.